namespaced Quantity to SystemOfQuantities
replaced Quantity with SystemOfQuantities::Quantity
#load returns self to allow method chaining and assignment
SystemOfUnits is now a module, since it will not be instantiated
renamed SystemOfQuantities to ISQ, SystemOfUnits to SI
namespaced Unit to SI::Unit
refactored method_missing, implemented respond_to?, load!, clear!
add_prefix add_unit dont create dups, finders (static and dynamic) for prefixes and units, respond_to? implemented, removed duplicate unit definitions
refactored #<=> method, renamed spec vars from meter to metre
implemented comparable prefixes and hash method
renamed spec variables meter to metre